ENERGY STORAGE

FLOW BATTERY

Student names:
 Noor Ali Mohammad Qasim.
 Ala’a Meafeq Ahmed Almanaseh.
 Roa’a Ahmad Abu AlkhaI.
 Nada Emad Abu-Ghazaleh.
Introduction
Large-scale electrical energy storage systems are becoming
more necessary as the production of intermittent energy
sources like wind and solar rises quickly. These systems will
help better balance the supply and demand for these
renewable energy sources. Additionally, by load leveling, large-
scale energy storage can raise the annual load factor, which is
calculated by dividing the annual mean power by the maximum
three-day mean power. Large-scale facilities have historically
employed pumped hydro for load leveling, but this is only
feasible in a few numbers of places.

For electric power providers, flow batteries are particularly

appealing for these leveling and stabilization applications. They
are helpful for electric power users as well, such industries and
office buildings, who need higher capacity, uninterrupted
power, or backup power. With an emphasis on the vanadium
chemistry, this paper will introduce the fundamental idea
behind the flow battery and cover both current and future
applications.

What are flow batteries?

Flow batteries are a type of electrochemical energy storage
system, consists of two chemical components dissolved in a
liquid and separated by a membrane.

Regenerative fuel cells have been used to describe flow

batteries, which function similarly to fuel cells. The use of an
electrolyte that flows across the surface of a nonreactive
electrode distinguishes these batteries from others. Flow
batteries can discharge for up to 10 hours at a time, making
them the perfect energy storage option for large-scale
applications. When compared to other battery types, which can
only drain for up to two hours at a time, this is a significant
discharge time. Their distinctive architecture is the primary
distinction between them and other rechargeable battery
types, such as lithium ion batteries.

Electrons flow via electrochemical cells and a membrane that

divides the electrons as they pass through the two outside
tanks used in this design to separate the fluid. The amount of
power that can be produced depends on the size of these
outside tanks; the larger the tank, the more electricity that can
be produced.

Utility, micro grid and electric vehicle applications for flow

batteries (EVs). Larger applications, such as utilities or micro
grids (smaller electric grids that may function independently),
frequently use flow batteries due to their lengthy discharge
capacity. Flow batteries are the best option for EVs because of
their speedy "recharge" or replacement of electrolyte liquid.
Iron and vanadium are two materials that are frequently used
in flow batteries.

Difference between flow batteries

and other types of batteries:
The main difference between flow batteries and other
rechargeable battery types is the aqueous electrolyte
solution normally found in other batteries is not stored in
the cells around the positive electrode and negative
electrode. Instead, the active substances are stored in
external tanks and pumped towards the flow cell membrane
 and power stack. The larger the storage tanks, the more
electricity can be generated.

Flow batteries characteristics:

Flow batteries have a variety of appealing qualities, including:

 Power/Energy Density:  The solubility of ions in the

electrolyte solutions controls energy density. Also take
note that the flow battery approaches its theoretical
maximum of energy density as the volume of the cell
components decreases in relation to the volume of the
electrolytes. Higher capacity systems are therefore more
effective in this regard because the electrolyte, which
directly stores energy, makes up the majority of the
weight. Capacity may be expanded by simply enlarging
the electrolyte storage tanks because it is independent of
the component that generates power, similar to an
internal combustion engine and gas tank. The chemical
species are kept outside the cell, allowing for
independent scaling up of power and capacity criteria in
flow batteries. The voltage and current density affect how
much electricity each cell produces. Flow batteries are
typically operated at 50 mA/cm2, which is roughly the
same as convection-free batteries. [3] The internal
resistance of the cell might be greatly decreased, though,
by material advancements in the electrodes and
membrane. Some redox flow cells have been able to
attain current densities as high as 80 mA/cm2 of
electrode area in a 50 kW total output system by using a
thinner membrane while preserving ion selectivity. [4]
However, because the volume covered by the aqueous
reagents/products is so much bigger, as is demonstrated
in Table 1 below, the overall power density still remains
poor when compared to lead-acid and lithium-ion
 batteries. As a result, the main flaw with flow batteries is
their low energy and power density, which future
research has a great opportunity to address.

Batteries Energy Density (Wh/L) Power Density (W/L)

Bromine-polysulfide 20-35 60
Vanadium-vanadium 20-35 60-100
Vanadium-bromine 20-35 50
Zinc-bromine 20-35 40
Zinc-cerium 20-35 50
Lead-acid 60-80 230
Lithium-ion 150-200 275
Nickel metal hydride 100-150 330

Table 1: Battery Comparison, the first five are flow batteries.

 Efficiency: the average ranges are 62-73% voltage

efficiency, 80-98% coulombic (charge) efficiency, and 66-
75% energy efficiency. Efficiency varies greatly depending
on the chemistry, state of charge, and process
circumstances.

 Since energy is stored in the electrolyte, it is possible to

size the storage capacity independently of the power.

 During use, the electrodes don't undergo any chemical

changes.

 Battery parts can be changed both during use and at the

end of their useful lives, prolonging operational lifetime.
How does flow battery work?
A flow battery is an electrochemical conversion device that
uses the energy differences between the oxidation states of
certain elements.

In tanks of liquid electrolyte that are circulated past electrodes

to extract the electrons, the flow batteries store electricity. The
electrolyte is recharged using grid input, wind turbines, or solar
or photovoltaic panels during the charging phase. Throughout
the storing period, the electrolyte is kept in the tank. Pumping
liquid electrolyte through electrodes during the discharging
phase allows for the extraction of electrons and the generation
of electricity.
Types of flow batteries:
1. Redox flow batteries

A flow battery or redox flow battery is a type of electrochemical

cell where the chemical energy is provided by two chemical
components dissolved in fluids within the system and
separated by a membrane.

The ion exchange (accompanied by the flow of electric current)

occurred through the membrane while both liquids circulated
in their respective spaces. The cell voltage is determined
chemically by the Nernst equation and in practical applications
ranges from 1.0 to 2.2 volts.

Types of redox batteries

 Several types of redox flow batteries exist, including: zinc

bromide, polysulfides, and zinc-cerium-but escaped
environmental considerations, vanadium-flow batteries
are now more common.

2. Hybrid flow battery

One of the active materials is stored within the

electrochemical cell, whiles the other remains in the liquid
electrolyte and is stored externally in a tank, an approach
combining features of conventional secondary batteries and
flow batteries.
 Types of hybrid batteries

 The hybrid flow battery classified into three types:

Zinc-Bromine (Zn-Br), Zinc-Cerium (Zn-Ce) and Iron Salt.

The most common type is Zinc-Bromine (Zn-Br).

Advantages of flow batteries:

 The power capacity (dependent on the size of the
electrodes) and the power capacity (dependent on the
size of the external storage tanks) of the flow batteries
are independent. This allows the design to meet the
specific needs of applications.
 Containing giant tanks of electrolyte, high-capacity flow
batteries have the ability to store a large amount of
electricity.
 The electrodes only collect current and do not participate
in chemical reactions; hence it is stable and durable.
 Flow batteries have the ability to discharge and recharge
at the same time without affecting cycle life.
 Flow batteries have a long cycle life and low maintenance.
Disadvantages of flow batteries:
 Flow battery systems are complex. They require
pumps, sensors, flow and power management, and
secondary containment vessels.

 The high cost of the materials used in them, such as

vanadium.

References:
 N. Tokuda et al., "Development of a Redox Flow Battery System,"
Sumimoto Electric Industries, SEI Technical Review 50, 88 (2000).
 C. Ponce De León, "Redox Flow Cells for Energy Conversion," J.
Power Sources 160, 716 (2006).
 T. Nguyen and R. F. Savinell, "Flow Batteries," Interface 19, No. 3,
54 (2010).
 M. R. Mohamed, S. M. Sharkh and C. Walsh, "Redox Flow
Batteries for Hybrid Electric Vehicles: Progress and Challenges," in
IEEE Vehicle Power and Propulsion Conference VPPC '09, 7 Sep
09, p. 551.
 ScienceDirect; Flow Battery; Flow Battery - an overview |
ScienceDirect Topics
 Introduction to Flow Batteries: Theory and Applications; Bhaskar
Garg; March 22, 2012; coursework for PH240; Stanford
University; Introduction to Flow Batteries: Theory and
Applications (stanford.edu)